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Distinction of sialyl anomers on ESI- and FAB-MS/MS: stereo-specific fragmentations

Reputable Mentor II
Reputable Mentor II
Ohashi Y, Kubota M, Hatase H, Nakamura M, Hirano T, Niwa H, Nagai Y.
J Am Soc Mass Spectrom. 2009 Mar;20(3):394-7.
An anomeric pair of the lysoglyceroganglioside 1-O-octadecyl-3-O-(N-acetyl)neuraminyl-sn-glycerol sodium salt was studied to see if sialic anomers were distinguishable by mass spectra. It was evident that, in the electrospray ionization and fast-atom bombardment product-ion spectra: (1) in the positive MS(2) product-ion spectrum, the beta- anomer showed an unexpected aglycone-side sodiated sodium alkoxide ion, which was absent for the alpha-anomer; (2) in both polarities the beta-anomer showed dehydration much more easily than the alpha-anomer; and (3) in the negative MS(2) product-ion spectrum, the beta-anomer also readily showed decarboxylation. Our hypothesis is that, although several easily interconvertible conformations may be allowed, the one having the large aglycone in the equatorial orientation affects the collision-induced dissociation fragmentations.
Department of Applied Physics and Chemistry, The University of Electro-Communications, Tokyo, Japan.
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